The Zipper rethinks urban housing with a single-stair, split-level core. Unoccupied circulation space is minimal. Most of the conditioned space supports the units. The Zipper challenges conventional multi-family designs by unlocking high-performance, low-carbon housing for narrow urban lots – increasing density, efficiency, and affordability. By integrating Passive House principles, modular construction, and renewable energy, the building exceeds strict energy and sustainability targets while remaining replicable across varied urban contexts. Its flexible, code-conscious approach makes the Zipper a viable model for cities looking to modernize zoning regulations and expand housing options without sacrificing livability.
Like many cities, parts of Denver have a standard north-south grid. Long, narrow 25-foot wide lots favor single-family homes or slot homes (side-by-side walk ups). A single-stair point access block, like the Zipper, centers units around one stairway within a multi-family dwelling. Larger buildings can have multiple clusters with shared vertical access, as shown above. In addition to Denver, Seattle, Chicago, New York, and Los Angeles allow single-point access block housing.
PERFORMANCE: The Zipper meets Passive House standards as confirmed through WUFI Passive energy modeling. The solar energy study further refines the envelope, guiding the selection of high-reflective materials and strategic window sill depths to balance daylight and heat gain across seasons. PV panels, elevated on canopies, provide on-site energy production while offering shade for rooftop equipment. Balconies are thermally broken from the main structure, ensuring continuous insulation and reducing thermal bridging, contributing to an efficient, high-performance envelope.
FLEXIBILITY: A standard layout and simple wall assemblies allow for replication. Pre-fabricated/identical bathroom and kitchen modules can increase affordability, stacking as cores. With consolidated circulation, units range from 1-3 bedrooms despite the narrow footprint, even accommodating balconies.
Critics of single stair housing blocks often cite fire as a reason to prioritize double-loaded corridors with two means of egress. But with limited floor areas, short travel distances, and maintaining heights lower than a ladder truck, the Zipper design (fully sprinklered) can be very safe.